Maintenance

The department is responsible for all interstates and primary highways. There are two types of primary highways: U.S. highways, that are designated by a black and white sign along the roadway with a number inside a shield. State highways, that are designated by a black and white sign with a number inside a circle.

The Iowa DOT is responsible for the interstate system, all federal highways, and all state highways across Iowa. In some instances where a federal or state highway goes through a city, the Iowa DOT would be responsible but in several communities, agreements have been made between the Iowa DOT and the city to have the city remove the snow and ice from the portion of the highway that passes through the city. These agreements can help reduce costs to the Iowa DOT and provide for more continuity of service on the highways. The Iowa DOT is not responsible for county blacktops or gravel roads as they are the responsibility of the respective county engineer’s office. Cities are responsible for snow and ice removal on the streets within the city's jurisdiction.

The department is responsible for snow removal for approximately 24,500 lane-miles of roadway. With approximately 900 trucks, the average time to complete a snow route is approximately two to three hours, but some can take as long as four hours. There is also the amount of time needed to load and unload the truck with deicing materials. If you are driving, it could be that the plow truck is just ahead or behind you. If you would like to see where the plows are active, the 511 website shows our plows’ GPS position.

The department uses about 150,000 tons of salt on an “average” season. This amount varies considerably from winter to winter, depending on the weather. The statewide average cost for the last few years has been about $83 per ton, but varies by location and year.

The department has specialized roadside weather reporting stations collecting pavement surface and atmospheric information. The systems measure air and pavement temperatures, relative humidity, wind speed and direction, subsurface temperatures, and many have cameras. This information is useful for planning plowing operations and material application amounts.

Pavement temperature is what drives most of the melting action on the road. Air temperatures are not usually good indicators of what the actual temperature is of the road surface. During the fall, the pavement is often warmer than the surrounding air because of the warm soil. During the spring, the reverse may be true and pavement temperatures can be colder than the air because the soil is still frozen from the long winter temperatures. The sun also has a strong influence on the pavement temperatures that will help heat the pavement and help the melting process. The difference between air and pavement temperatures can often differ by as much as 20 degrees Fahrenheit.

Often, it is because some storms are easy to manage, and other storms are difficult. One of the biggest factors that determine performance is the type of storm (ice vs. snow vs. blowing snow) and temperatures. Storms with low temperatures can be difficult because deicing chemicals become less effective at the lower temperatures. It takes nearly eight times as much salt to melt a pound of ice at 20 degrees Fahrenheit than at 30 degrees Fahrenheit. Storms with high winds are a challenge because the snow quickly blows back onto the roadway after the plows pass. There are reportedly more than 65,000 combinations of winter storms that can hit Iowa during the winter, and each pose unique problems to snowplow operators.

It looks like water, but it’s actually salt brine. You will often see us do this when there is a storm coming soon. Spraying a liquid salt-brine solution on the roadway will help keep future snow and ice from bonding to the pavement. The water will dry off and the remaining salt acts as a barrier so the snow and ice does not form a strong bond to the pavement. Studies show that under extremely cold conditions ice frozen to concrete has a stronger bond than concrete alone. We also spray salt brine on bridge decks the afternoon before a predicted frost. The daytime application of the salt solution helps prevent frost from forming on bridge decks throughout the night.

The department has approximately 900 snowplows available throughout the state. The DOT also has 33 tow plows, 10 heavy duty snow blowers, and 111 tractor/loader blowers that assist with snow removal.

Typically plows are operating 24 hours a day, but at times reduced numbers may be available as operators are given time off for rest. If weather conditions are so severe that progress is not being made, trucks may be pulled off the road until conditions improve.

The local plow operators and supervisors report road conditions as they change. See current road conditions on www.511ia.org.

The department has two basic categories of trucks used in winter operations; heavy duty and medium duty. Heavy duty trucks have 3 axles and a capacity of 8 cubic yards, and the medium duty dump truck has 2 axles and a capacity rating of 4 cubic yards.

Typically when the plow is down snowplows operate at 20-35 mph, but are often moving even slower if the snow is deep or conditions warrant a slower speed. Always be on the lookout for the blue-white-amber flashing warning lights during a winter storm because the lights warn you of a slow-moving snowplow ahead of you.

Potholes are the holes in the roadway that can be various shapes and sizes caused by the expansion and contraction of water that has entered the pavement structure from a crack in the surface. When the water freezes, it expands, and forces the pavement to expand, bend or crack, which weakens the material. Then when ice melts, the pavement contracts and the new cracks leave more places where water can get in. If the water freezes and thaws over and over, the pavement may get very weak.

As the weight of cars and trucks pass over the weak spot in the road, pieces of the roadway material weakened by the freeze-thaw effect get displaced or broken down from the weight, creating the pothole.

What happens when salt is brought into the picture? Water will freeze at 32 degrees Fahrenheit. When salt is used, it lowers the temperature that water will freeze, creating an artificial freeze-thaw cycle to occur. This happens more in the spring because of the melting that takes place and because the temperatures go between above freezing and below freezing very frequently and allows many freeze-thaw cycles to weaken the pavement.

For corrosion to take place, there are three things that are needed before it happens — metal, air and water. Metal things are usually exposed to air, but when water gets introduced into the picture corrosion can begin. Water gets into an area of metal that is weak or not protected from paint or oil. When there is a weak spot in the metal of your vehicle and water finds a way to get to the metal, corrosion will begin. The salt or deicing chemical is a corrosion accelerator. It is not necessary for corrosion to take place, but it speeds the process of corrosion along. Therefore, when you see corrosion on a vehicle, it means the metal has been exposed to air and water. Salt from the road may have accelerated the corrosion process and made the corrosion worse.